1. Field of the Invention
The present invention relates to a spring sheet that supports a coil spring.
2. Description of the Related Art
In many cases, a strut type suspension apparatus is used as the suspension apparatus for such a vehicle as a motor car. An example of the suspension apparatus 1 is shown in FIG. 15.
The suspension apparatus 1 comprises a damper 2 and a coil spring 7. The damper 2, which serves as a strut, extends through the region defined by the coil spring 7. The lower end of the coil spring 7 is supported on a lower spring sheet 4, while the upper end thereof is held down by an upper spring sheet 5. The lower spring sheet 4 is shaped like a funnel and is attached to the outer circumferential surface of the outer casing of the damper 2. The upper spring sheet 5 is shaped as a disk and is fixed to the upper end (i.e., the piston end) of the damper 2 together with an upper mount 6 assembled to a car body. A wheel is attached to the lower portion of the damper 2 by means of a hub carrier.
When the damper 2 contracts, the coil spring 7 is applied with a compressive load by the lower spring sheet 4 and the upper spring sheet 5. Sheet surfaces 4a and 5a of the lower spring sheet 4 and the upper spring sheet 5, which the coil spring 7 come into contact with, are formed in such a manner as to continuously extend in accordance with the shapes of spring end portions 7a and 7b of the coil spring 7. For example, where the spring end portions have no winding pitch amount (i.e., the case where the pitch amount is 0 mm/winding), the sheet surfaces are formed to be flat, as indicated by the thick line xe2x80x9cfxe2x80x9d in FIG. 16. Where the spring end portions have a winding pitch amount, the sheet surfaces are formed to extend spirally at an angle corresponding to the pitch amount of the spring end portions, as indicated by the thick line xe2x80x9csxe2x80x9d in FIG. 17.
For easy assembly of the suspension apparatus 1 into the body of an automobile or the like, the spring sheets 4 and 5 usually support the coil spring 7 so that the central axis xcex1 of the coil spring 7 may be inclined with reference to an axis of actual load application, such as an actual application axis xcex2 of an external force extending between a king pin and the upper end of the damper. In this condition, the damper 2 and the coil spring 7 jointly dampen a shock applied from the front wheels.
However, the pitch amount of the coil spring changes so that the compressed amount varies in accordance with a change in the compressive load. On the other hand, the sheet surfaces 4a and 5a are not deformed in accordance with a change in the pitch amount of the coil spring 7. As a result, the contact areas and contact positions between the spring end portions 7a, 7b and the sheet surfaces 4a, 5a may vary in accordance with changes in the compressive load, which serves to compress the coil spring 7.
In addition, the coil spring 7 inevitably undergoes variations arising from the manufacturing tolerance. In FIGS. 16 and 17, such variations are represented by undulated portions 7c which indicate a phenomenon wherein the coil wire is shifted from its right position in the direction of the central axis xcex1 of the coil spring 7 at the spring end portion 7a, and a pitch tolerance between the spring end portion 7a and the sheet surface 4a. 
Where the undulated portions 7c exist, they extend along the sheet surfaces 4a and 5a when the coil spring 7 is compressed. When the displaced portions 7c extend, the contact range (contact area) between the spring end portion 7a and the sheet surface 4a varies. Where the pitch tolerance exists, the contact position between the spring end portion 7a and the sheet surface 4a varies in the process of compressing the coil spring.
When the contact range and positions between the spring end portion 7a and the sheet surface 4a vary, the distribution of the contact reaction applied from the spring sheet 4 to the coil spring 7 is changed. When the distribution of the contact reaction changes, the load axis along which the resultant of loads is exerted on the coil spring 7 changes in direction, accordingly. The coil spring 7 of the suspension apparatus 1 shown, for example, in FIG. 15 is assembled in such a manner that the central axis xcex1 is shifted from the actual application axis xcex2 in which a load is applied actually. Owing to this structure, a change in the direction of the load axis along which the load is exerted on the coil spring 7 affects the balance between the force component applied in the sliding direction of the damper 2 and the force component applied in the direction traversing the sliding direction. Since the force acting in the direction traversing the sliding direction serves as a bending moment with reference to the sliding direction of the damper 2, the sliding resistance of the damper 2 varies. As a result, the dynamic characteristics of the suspension apparatus 1 vary, failing to provide intended performance.
A spring sheet according to the present invention is intended to control the direction of the load axis of the contact reaction applied to the spring end portion of a coil spring, independently of the compressed state of the coil spring.
To this end, the spring sheet according to the present invention is provided with a plurality of receiving portions on its sheet surface, and the receiving portions come into contact with the spring end portion of a coil spring in a discrete fashion.
At specific positions, the spring end portion is locally received by the receiving portions. With this structure, even if the displaced portion extends when the coil spring compresses, it does not undesirably touch the sheet surface. In addition, the coil spring does not contact the sheet surface at undesired portions even if the coil spring has characteristics deviating from design values.
The receiving portions of the spring sheet are located at positions which sandwich the central axis of the coil spring from both sides even when the coil spring is shifted from the central axis of the spring, and at axial positions which permit the load axis of the contact reaction distribution to align with the actual application axis of an external force when the coil spring comes into contact with a projection.
With this structure, even if the coil spring is assembled in such a manner as to be shifted from the actual application axis of an external force, the spring sheet allows the coil spring to generate a reaction force in the direction of the actual application axis, and prevent it from generating a lateral force, which would adversely affect movement along the actual application axis.
In the case of a spring sheet in which the receiving portion on one side is made up of a plurality of sections, the load axis of the coil spring is inclined to align with the actual application axis of an external force exerted on the coil spring.
In the case of a spring sheet can be separated into a spring receiving member on which a sheet surface is formed, and a bracket which supports the spring receiving member, the specifications of the spring sheet can be changed by replacing the spring receiving portion with another. That is, the spring sheet is applicable to suspensions of different specifications by selectively employing different spring receiving members.
In the case of a spring sheet that supports the spring end portion of a coil spring by means of a plurality of receiving portions arranged in the winding direction of the coil spring, the coil spring is supported on the plurality of receiving portions without being adversely affected by the manufacturing tolerances of the coil spring and the spring sheet. Therefore, the load axis of the coil spring can be easily orientated in a desired direction.
The receiving portions of the coil spring are arranged in such a manner that the load axis, which indicates the direction in which the resultant of forces acting between the receiving portions and the coil spring is applied, is made to align with the actual application axis along which a load is exerted on the coil spring.
The receiving portions are arranged along an imaginary plane passing the actual application axis and the central axis of the coil spring and located at positions sandwiching the central axis from both sides. The center of the force the coil spring receives from at least one of the receiving portions on each side is located along the imaginary plane.
Of the receiving portions, at least one receiving portion close to the actual application axis is shifted along the central axis in a direction in which the coil spring is compressed, as compared to at least one receiving portion located away from the actual application axis.